European patent application EP 1 016 787 A2 discloses a gas-supply system as well as an appertaining operating method of the above-mentioned type. This prior-art gas-supply system comprises a gas-carrying pipeline, a controllable compressor arranged in the pipeline and a consumer namely, a gas turbine. connected to the pipeline and located downstream from the compressor. In order to actuate the compressor, a control unit in the form of a regulator is provided that regulates the compressor as a function of a setpoint/actual-value comparison of the discharge pressure of the compressor. For regulation purposes, the regulator can change the rotational speed and/or the guide vane setting of the compressor. The actual discharge pressure of the compressor can be measured in a conventional manner at the compressor outlet. In contrast to this, normally speaking, the set point discharge pressure of the compressor is permanently preset, whereby this preset value depends on the location of the gas turbine, particularly on the lowest ambient temperatures that can be expected. Furthermore, the predetermined setpoint discharge pressure of the compressor is derived from the maximum output of the gas turbine as well as from the maximum gas temperature and from the lower caloritic value of the gas.
Moreover, in the prior-art gas-supply system, a throttle element is installed in the pipeline upstream from the compressor, said throttle element being actuated by means of a separate regulator. When the pressure in the pipeline changes, the throttle element can be employed to continuously regulate the desired admission pressure for the compressor that allows the compressor to adjust the discharge setpoint pressure of the compressor. In this manner, the compressor can be continuously operated at a high output, particularly at its rated output. This, however, is not always sensible for energy reasons.
Here, in particular, compressors having a fixed compression ratio are frequently employed. If the pressure in the pipeline increases, the discharge pressure can reach impermissibly high values if the admission pressure is not appropriately adjusted down by means of the throttle element located upstream. Such a compressor operates continuously at full load or at the rated load.